Calculation of the Truss Member

[yw21]

Homework Statement

Calculate the type and magnitude of the forces in the following member.
i) AB
ii) FG
iii) BC

Homework Equations

ƩFx = 0,
ƩFu = 0,
ƩM = 0

The Attempt at a Solution

I have calculated the AB and BC which are 80kN and 100kN respectively by using
Take moment at G :
(-80 * 12) + (60 * 8) + (40 * 4) + (FAB *4) = 0, and AB is equal to 80kN
Take moment at H:
(-80 * 8) + (60 * 4) + (FBC *4) = 0, and BC is equal to 100kN

Am I right with the concept?

Moreover, I am concered for the calculation of FG. How can I calculate the FG?
Thank you~~~

 

[yw21]

Moreover, the vertical force Fy and Ky are the same as 80kN

 

[pongo38]

I think you are numerically correct but have not assigned a sign to the forces obtained. I think you have mentally done what you are supposed to do, but not stated it or drawn it. The essential step was to cut the structure and replace the cut ends with unknown forces, before applying the three equations of equilibrium to the free body diagram obtained by cutting. To obtain force FG, try cutting around joint F in a complete circle (as distinct from the - implied - straight line cut you used to get the other forces)